From Freenode #xfce
https://iwf1.com/review-xfce-4-13-desktop-environment-a-noticeable-difference-from-its-predecessor/
please note section "Xfce 4.13 Finally Eliminates Screen Tearing" That comes from improvements to xfwm4
For those with lxqt (as well as xfce) note https://git.xfce.org/xfce/xfwm4/commit/?id=b3e2686bea4aec26fe95db4938abc3820308e265
looks nice.
Note: xfce 4.13 is neither in Stretch nor in Sparky's xfce spin, but should be seen soon in testing-Buster when stretch goes stable. In testing and sid xfce4 is still at 4.12-3